CS251 – Software Engineering Lectures 18: Intro to DP

1. و ابتغ فيما آتاك الله الدار الآخرة و لا تنس نصيبك من الدنيا CS251 – Software EngineeringLectures 18: Intro to DP Slides by Rick Mercer, Christian Ratliff, Oscar Nierstrasz and others

2. Outline • Introduction to Design Patterns • Template Method Pattern • Decorator Pattern

3. Resources • The Swing Tutorial http://docs.oracle.com/javase/tutorial/uiswing/index.html • List of patterns: http://www.oodesign.com/

5. 1. Background1 • Search for recurring successful designs – emergent designs from practice (via trial and error) • Supporting higher levels of reuse (i.e., reuse of designs) is quite challenging • Described in Gama, Helm, Johnson, Vlissides 1995 (i.e., “gang of 4 book”) • Based on work by Christopher Alexander (an Architect) on building homes, buildings and towns.

6. Background2 • Design patterns represent solutions to problems that arise when developing software within a particular context. E.g., problem/solution pairs within a given context • Describes recurring design structures • Describes the context of usage

7. Background2 • Design patterns represent solutions to problems that arise when developing software within a particular context. E.g., problem/solution pairs within a given context • Describes recurring design structures • Describes the context of usage

8. Background3 • Patterns capture the static and dynamic structureand collaborationamong key participants in software designs • Patterns facilitate reuse of successful software architectures and designs.

9. Elements of Design Patterns • Design patterns have four essential elements: • Pattern name • Problem • Solution • Consequences

10. Pattern Name • A handle used to describe: • a design problem • its solutions • its consequences • Increases design vocabulary • Makes it possible to design at a higher level of abstraction • Enhances communication • “The Hardest part of programming is coming up with good variable [function, and type] names.”

11. Problem • Describes when to apply the pattern • Explains the problem and its context • May describe specific design problems and/or object structures • May contain a list of preconditions that must be met before it makes sense to apply the pattern

12. Solution • Describes the elements that make up the • design • relationships • responsibilities • collaborations • Does not describe specific concrete implementation • Abstract description of design problems and how the pattern solves it

13. GoF: Design Patterns Creational: Abstract Factory Builder Factory Method Prototype Singleton Behavioral: Chain of Responsibility Command Interpreter Iterator Mediator Memento Observer State / Player-role Strategy Template Method Visitor Structural: Adapter Bridge Composite Decorator Façade Flyweight Proxy

15. Outline • Introduction to Design Patterns • Template Method Pattern • Decorator Pattern

16. Template Method Pattern • A template is a preset format, used as a starting point for a particular application so that the format does not have to be recreated each time it is used. • MS Word Templates • Java Generics • C++ Templates

17. Template Method Pattern • A template method defines an algorithm in a base class using abstract operations that subclasses override to provide concrete behavior.

18. Intent • Define the skeleton of an algorithm in an operation, deferring some steps to subclasses. • Template Method lets subclasses redefine certain steps of an algorithm without letting them to change the algorithm's structure.

19. Implementation

20. Usage • Implementing the invariant parts of an algorithm once and leave it up to subclasses to implement the behavior that can vary. • Refactoring is performed and common behavior is identified among classes. A abstract base class containing all the common code (in the template method) should be created to avoid code duplication.

21. ? Example 1 • We have to develop an application for a travel agency. • The travel agency is managing each trip. • All the trips contain common behavior but there are several packages. • Each trip contains the basic steps: • The tourists are transported to the holiday location by plane/train/ships,… • Each day they are visiting something • They are returning back home.

22. Example 1See Code

24. Outline • Introduction to Design Patterns • Template Method Pattern • Decorator Pattern

25. Decorator Pattern • Read it in readings R13

26. Readings • Readings 13 and 14 • Read code sets …….

27. Top 10 Books Programmers Read • Code Complete by Steve McConnell (2E, 2004). • The Pragmatic Programmer by Andrew Hunt and David Thomas (1999). • Structure and Interpretation of Computer Programs by Abelson, Sussman, and Sussman (2E, 1996). • The C Programming Language by Brian Kernighan and Dennis Richie. CPSC-4360-01, CPSC-5360-01, Lecture 8

28. Top 10 Books Programmers Read • Refactoring: Improving the Design of Existing Code by Martin Fowler, Kent Beck, John Brant, and William Opdyke (1999). • Design Patterns: Elements of Reusable Object-Oriented Software by Gamma, Helm, Johnson, and Vlissides (1994). The "Gang of 4" book. • The Mythical Man-Month by Frederick Brooks (1995). CPSC-4360-01, CPSC-5360-01, Lecture 8

29. Top 10 Books Programmers Read • The Art of Computer Programming, Volume 1: Fundamental Algorithms (3rd Edition, 1997) by Donald Knuth. • Compilers: Principles, Techniques and Tools 2E by Aho, Lam, Sethi, and Ullman (2006). CPSC-4360-01, CPSC-5360-01, Lecture 8

30. Top Magazines Recommended to Read • Dr Dobbsالله يرحمها • IEEE Software CPSC-4360-01, CPSC-5360-01, Lecture 8